Nobody expected the Soviet regime to end so suddenly. Most revolutions die with a whimper rather than a bang. Some people say that the events of 1985-91 were a revolution in themselves. This is not quite right. But the speed with which the system fell apart took everybody by surprise, and this seemed to earn the name.

In 1985 the Soviet Union seemed as permanent as any state. None of the problems Gorbachev intended to address threatened the existence of the Soviet system.

The economy was in trouble. The all-important revenues from oil declined dramatically, as prices fell from $37 a barrel in 1980 to $14 in 1986. More investment was needed in the older Soviet oil-fields, but more than half the government's expenditure was eaten up by the military.

To fill the holes in its budget the government took money out of people's savings, increased vodka sales, and built up a massive deficit. People grumbled about low pay, poor living conditions, shortages of food and consumer goods.

But the economy had been much worse at more unstable periods of Soviet history. The Soviet population was used to shortages, and there were no signs of mass protest.

In other words, the regime could have soldiered on. There was no pressing need for radical reform. Authoritarian regimes can survive - not for ever but certainly for decades - with worsening economies. Many have done so with circumstances worse than in the Soviet Union during the 1980s. If there was a 'crisis' in the USSR, it was perceived mainly by the Soviet élites.

It was Gorbachev's reforms that pushed the system into revolutionary crisis, not a crisis in the system that brought about reforms. As Alexis de Tocqueville wrote in the nineteenth century. 'the most dangerous moment for a bad government is when it begins to reform.'